<!DOCTYPE html>
<html style="height: 100%">
  <body style="height: 100%">
    <table style="height: 50%; width: 50%">
      <tr>
        <td id="x" style="position: relative; top: 25%; left: 25%">
          <div style="position: absolute; left: 0; right: 0; top: 0; bottom: 0;
                      background: green"></div>
        </td>
      </tr>
    </table>
  </body>
</html>
